A vocal opponent of the unequal distribution of wealth, the itinerant activist has spent time in several countries across the world,
railing against the callousness and injustices of governments, the negligence of the upper classes, and trying to forge a transnational people’s movement.
(A) railing against the callousness and injustices of governments, the negligence of the upper classes, and trying to forge a transnational people’s movement -> We have list items "railing", " the negligence" and "trying" are not parallel. Incorrect.
(B) to rail against the callousness and injustices of governments and the negligence of the upper classes, and trying to forge a transnational people’s movement -> We need -ing modifier to start with. Incorrect.
(C) railed against the callousness and injustices of governments, the negligence of the upper classes, and tried to forge a transnational people’s movement -> We need -ing modifier to start with. Incorrect.
(D) railing against the callousness and injustices of governments and the negligence of the upper classes, and trying to forge a transnational people’s movement ->
We have list items "railing", and "trying" are parallel. Let's keep it.(E) railing against the callousness and injustices of governments, the neglecting of the upper classes, and trying to forge a transnational people’s movement -> We have list items "railing", " the neglecting" and "trying" are parallel. But, meaning wise, "the neglecting of the upper classes" is not a list item, rather "railing" is a list item. Incorrect.
So, I think D.